PROJECT SUMMARY Heart failure is a major cause of morbidity and mortality worldwide, currently affecting an estimated 6.5 million adults in the US alone and contributing to $21 billion in health care costs. The aim of this proposal is to understand the mechanisms of heart failure recovery. We have clinical evidence that heart failure recovery involves a reduction in interstitial myocardial fibrosis and an increase in microvascular density. Our library of human samples from Left Ventricular Assist Device (LVAD) implantation/explantation represent a convenience sample to examine the mechanisms of recovery. In these patients, the LVAD implantation (and unloading of the heart from hemodynamic forces) promotes some improvement in ventricular function (as assessed by echocardiography) that is associated with decreased interstitial fibrosis and increased vascular density. Based on clinical and pre-clinical data, we hypothesize that recovery from heart failure is (at least in part) a vascular recovery. The vascular recovery may involve mesenchymal-to-endothelial transition (MEndoT), that is, the transdifferentiation of cardiac fibroblasts (or other mesenchymal cells) into endothelial cells. Furthermore, we have evidence that MEndoT may require a glycolytic switch that directly affects DNA accessibility and cellular plasticity. In our first aim, we will characterize the physiological, cellular, and molecular hallmarks of heart failure recovery in a unique mouse model. In the second aim, transcriptional profiling of disaggregated mouse hearts as well as human cardiac tissue obtained pre- and post-LVAD implantation will be combined with bioinformatics analyses to predict novel genes in heart failure recovery. In our third aim, we will confirm the genetic determinants discovered in the first aim using gain- or loss-of-function studies in vitro and in vivo. In addition, we will explore the role of the glycolytic switch in cell fate transitions and vascular recovery using bioinformatics analyses of our RNAseq data, confirmed with cell-specific and conditional gain- or loss-of-function studies of target genes (e.g. in metabolic pathways) in vitro and in vivo. The intent of this proposal is to generate fundamental insights regarding heart failure recovery that may lead to a new therapeutic strategy.